Bolometer and method of producing a bolometer

ABSTRACT

A bolometer includes a membrane, a first spacer and a second spacer, the membrane including resistive and contact layers. At a side facing a foundation, the contact layer has a first contact region at which the first spacer electrically contacts the contact layer, and a second contact region at which the second spacer electrically contacts the contact layer. In this manner, the membrane is kept at a predetermined distance to the foundation. The contact layer is laterally interrupted by a gap, so that the contact layer is subdivided at least into two parts, the first part including the first contact region, and the second part including the second contact region, and no direct connection existing within the contact layer from the first contact region to the second contact region, and the resistive layer being in contact with the first and second parts of the contact layer.

The present invention relates to a bolometer and a method of producing abolometer, and in particular to a scalable microbolometer structure.

BACKGROUND OF THE INVENTION

A bolometer is a device for measuring the intensity of electromagneticradiation of a specific wavelength range (approx. 3-15 μm). It comprisesan absorber, which converts electromagnetic radiation to heat, and adevice for measuring an increase in temperature. Depending on a thermalcapacity of the material, there is a direct connection between an amountof radiation absorbed and the resulting increase in temperature. Thus,the increase in temperature may serve as a measure of an intensity ofincident radiation. Of particular interest are bolometers for measuringinfrared radiation, which is where most bolometers have a highest levelof sensitivity.

A bolometer may be used, in technology, as an infrared sensor, an imagerfor a night-vision device or as a thermal imaging camera.

A bolometer serving as an infrared sensor comprises a thin layer whichis arranged within the sensor in a thermally insulated manner, e.g. issuspended as a membrane. The infrared radiation is absorbed within thismembrane, whose temperature increases as a result. If this membraneconsists of a metallic or advantageously a semiconducting material, theelectrical resistance will change depending on the increase intemperature and on the temperature coefficient of resistance of thematerial used. Exemplary values regarding various materials can be foundin the paper R. A. Wood: “Monolithic silicon microbolometer arrays,”Semiconductor Semimetals, vol. 47, pp. 43-121, 1997. Alternatively, themembrane is an insulator (silicon oxide or silicon nitride) onto whichthe resistor has been deposited as a further thin layer. In otherimplementations, insulating layers and an absorber layer are disposed inaddition to the resistive layer.

The temperature dependence of metal layer resistances is linear,semiconductors as resistance material have an exponential dependence. Ahigh level of dependence is also to be expected from diodes as thermaldetectors with their current/voltage characteristic in accordance withI _(D) =I ₀*(Exp{eU _(D) /kT}−1)wherein T is the temperature, k is the Boltzmann constant, e is theelementary electric charge, I_(D) and U_(D) designate a currentintensity and voltage within the diode, and I₀ is a constant which isindependent of the voltage.

Bolometers may serve as individual sensors, but may also be designed asrows or 2D arrays. Rows and arrays nowadays are typically produced usingMicrosystems engineering methods in surface micromechanics on a siliconsubstrate. Such arrays are referred to as microbolometer arrays.

An advantageous wavelength of the infrared radiation to be detected isabout 8-14 μm, since this wavelength range comprises radiation of matterwhich has approximately room temperature (300 K). The wavelength rangeof 3-5 μm is also of interest because of a permeable atmospheric window.

An essential advantage of thermal bolometers over other (photonic) IRdetectors (IR=infrared) is that they may be operated at roomtemperature, i.e. uncooled.

The aim of further development is to arrange as many bolometer cells(pixels) as possible within one array. Thus, the array will have ahigher number of pixels and will provide a better resolution of an imageat the same total area (chip area) of the array. For example, anarrangement of 160×120 pixels is customary, 320×240 is also available,640×480 pixels (VGA resolution) has been announced and will be availableshortly, but only at considerable additional cost. At the same time itis useful to minimize the cost of the array so as to open up newmarkets, e.g. the field of motor vehicles.

The usual dimensions of a single pixel within the array comprise a pixelarea of 35 ×35 μm² to 50 ×50 μm². With 320 ×240 pixels, a chip area thusis at least 12.2 ×8.4 mm² =94 mm² (pixel area alone) plus an area for areadout circuit (e.g. an additional 2 mm per edge), in total approx. 137mm². Since a yield (the number of good chips in relation to the totalnumber on a disk, or wafer) sharply decreases as the chip areaincreases, economic production of such an array is hardly possible.Therefore, an increase in the number of pixels should entail a reductionof the pixel area. IR imagers of 35 ×35 μm² have been commerciallyavailable for some time now. As is described in the paper Mottin; “AboveIC Amorphous Silicon Imager Devices;” Leti 2005 Annual Review; Jul. 6,2005, pp. 1-18, arrays of 25×25 μm² are currently being developed. Buteven this surface area, which has already been scaled, leads to anunacceptably large chip area (estimated to be approx. 250 mm²) withimagers exhibiting VGA resolution. Further scaling of the pixel area istherefore absolutely essential. What is aimed at are pixels having pixelareas of approx. 15×15 μm². Further reduction in size will then conflictwith the fact that the optical systems which would be employed in such acase would have to be of very high quality, which, in turn, would onlybe feasible at very high cost.

Detection of infrared radiation within a microbolometer is based on thefact that the radiation heats a resistor which is thermally wellinsulated. Said resistor is temperature-dependent, and therefore itchanges its resistance as a function of warm-up. A change in resistanceis read out via an ROIC (read out integrated circuit). Typical increasesin temperature occurring at the resistor are within the range of severalmillikelvin (mK) per degree of temperature change in a target observed.For this increase in temperature at the bolometer to become possible,the resistor must be very well insulated thermally. This is achieved byarranging the resistor on a membrane (or by configuring it as a membraneitself) which is arranged, at a distance of several μm, above a disksurface and is connected to the disk surface, or to a substrate, only atfew points having low thermal conductivity.

FIG. 5 shows two bolometers in accordance with the prior art which aredescribed in R. A. Wood: “Monolithic silicon microbolometer arrays,”Semiconductor Semimetals, vol. 47, pp. 43-121, 1997. FIG. 5 a depicts asingle-level pixel which comprises a sensor 51, electronics 52 locatedon a substrate 54, and which has a pixel size 53. FIG. 5 b shows atwo-level pixel, wherein the electronics 52 are arranged below thesensor 51. This bolometer also corresponds to the prior art, and bycomparison with the bolometer shown in FIG. 5 a it comprises a higherfill factor (ratio of IR-sensitive area to the total area).

The membrane is generated, for example, in that the resistor or sensor51 is produced on a disk surface 55, and in that subsequently, theregion is undercut, so that a cavity 56 results. By locally removingsilicon (Si), for example, the thermal resistance between the resistoron the membrane 51 and the substrate 54 will increase. A readout circuit52 is integrated next to the membrane 51, and therefore takes upadditional chip area. Therefore, a structure of FIG. 5 b, wherein theresistor 51 is disposed in a second plane on a membrane above thereadout circuit 52, is more advantageous.

For measuring the resistance, two contact points are necessary. They maybe formed by arranging feed lines on portions of the membrane whichincline in the upward direction. The inclinations at the same time serveas spacers for the membrane. FIG. 6 shows a perspective view of acorresponding structure comprising a membrane 10, which consists of asupport 35 and a resistive layer 18. Such an arrangement is described inFIG. 2 of U.S. patent U.S. Pat. No. 5,688,699 (Nov. 2, 1997; B. T.Cunningham, B. I. Patel: “Microbolometer”). The membrane 10 is supportedby inclined support arms 20 comprising an electrically conducting layer32 and a thermally insulating layer 22. A contact of the membrane 10 viathe support arms 20 comprises an overlap 33, and the support arms 20extend into an epitaxial layer 14, where the corresponding circuit (notshown in the figure) is located. The epitaxial layer 14 is positionedbetween a substrate 12 and an insulating layer 24.

If the membrane 10 is planar (has no inclinations), the signals aresupplied via metallic plugs which at the same time serve as spacers.This structure is described in Tissot: “Uncooled Thermal Detectors forIR Applications;” Leti 5^(th) Annual Review; 2003, 11 pages and FIG. 7shows a perspective view of such a conventional structure having amembrane 10 on two contact plugs 26 a and 26 b, which is held at adistance 72 above a foundation 73. The membrane 10 having a size 75comprises a thickness 74, and the foundation 73 comprises a reflector.Thermal insulation from the foundation 73 is established via the bridges76 a,b. The foundation 73 has an ROIC input pad 77 located thereon bymeans of which the bolometer is contacted. Contacting of the membrane 10comprises an overlap 78 as compared to a diameter of the contact plugs26 a and 26b. This overlap 78 reduces the fill factor.

Optimum absorption of the IR radiation is achieved in that the membrane10 comprises a layer resistance in accordance with a spreadingresistance of an electromagnetic wave in air (377Ω/□), and is arrangedat a height of λ/4 (approx. 2.5 μm at the advantageous wavelength λ of,e.g., 8-14 μm) above a reflector 73.

US patent U.S. Pat. No. 5,912,464 cites such a bolometer and aproduction method, and FIG. 8 shows a portion of it. FIG. 8 a shows across section through a contacting of the membrane 10, thecross-sectional plane being shown by a dash-dotted line in FIG. 8 b witha viewing direction 81.

The contact plug 26 b contacts a terminal pad 77, and, at the same time,a contact layer 23. Further layers of the bolometers are a reflectionlayer 21, a sacrificial layer 22, the bolometer or resistive layer 27,and transition layers 24 and 25. The electrical contacting of theresistive layer 27 is established via the contact layer 23, and thetransition layers 24 and 25 serve for improved contacting of the contactlayer 23. The contact layer 23 extends in a meandering manner along theresistive layer 27 from a contact plug 26 a to the contact plug 26 b.The meandering implementation of the electrode layer 23 is shown by adashed line in FIG. 8 b. The meandering implementation of the electrodelayer 23 serves to improve the absorption of the infrared radiation.

It is also in this bolometer in accordance with the prior art that thecontact plug 26 b and the membrane 10 comprise an overlap. In FIG. 8 a,the overlap of the contact plug 26 b is marked by x, and the overlap ofthe membrane 10 is marked by y. The sacrificial layer 22 is only presentin the intermediate step shown here, and will be removed later on.

With corresponding processing, a sacrificial layer 22 of polyimide isapplied as a spacer to a disk having an integrated circuit (e.g. in CMOStechnology; not depicted in the figure). In the region of the contactplugs 26 a,b, the sacrificial layer 22 is opened in the form of acontact hole. In one implementation, which is shown in FIG. 8 a, ametallic contact layer 25 is deposited and patterned, and subsequently acontact metal for the contact plugs 26 a,b is deposited. This metal isetched such that it will overlap an edge of the contact hole. Theresistive layer 27 is deposited and patterned. At last, the sacrificiallayer 22 underneath the membrane 10 is removed, so that said membrane,which is held by the contact plugs 26 a,b, is suspended above thereflection layer 21, and, thus, a λ/4 absorber is formed.

FIG. 9 shows a conventional contacting as is also used in the example ofFIG. 8. The contact plug 26 b comprises an overlap x over a diameter zof the contact plug 26 b, and the membrane 10 comprises an overlap by avalue of y over the contact plug 26 b.

All embodiments described in U.S. patent U.S. Pat. No. 5,912,464, butalso the structures in accordance with U.S. patent U.S. Pat. No.5,688,699 or of document Tissot: “Uncooled Thermal Detectors for IRApplications;” Leti 5^(th) Annual Review; 2003, 11 pages have in commonthat the contact metal projects beyond the diameter z of the contactplug 26 b (distance x in FIG. 9). The membrane 10 itself projects evenfurther beyond (distance y in FIG. 9). The overlaps x and y represent acompensation for adjustment tolerances, they make sure that the regionof the contact plug (the contact area in FIG. 7) is not etched.

FIG. 10 shows how the bolometers in accordance with the prior art scalewhen the pixel size 75 is reduced. FIG. 10 a shows a top view of themembrane 10 with conventional contacting by means of the contact plugs26a and 26b, the membrane 10 being connected to the contact plugs 26 a,bvia the bridges 76 a,b. The bridges 76 a,b act as thermal insulation. Asis explained in FIG. 9, the membrane 10 overlaps the contact plug 26 bby the value of y, and the contact plug 26 b overlaps the diameter z ofthe contact plug 26 b by the value of x. In case of a reduction(scaling) of the pixel size 75, as is shown in FIG. 10 b, the size ofthe contact plugs is not scaled for technological reasons, and the fillfactor decreases accordingly. A reason for this is that the conventionalmanufacturing process is based on photosensitive polyimide as thesacrificial layer 22, and is therefore limited to a minimum hole sizewhich must be larger than approx. 3 μm (please see further commentsbelow).

FIG. 10 a also shows that, as is also visible in FIG. 7, the contactplugs 26 a,b with their contact to the membrane 10 are indeed relativelylarge, but that with a pixel of an edge length of approx. 50 μm, thesurface percentage thereof is relatively small. However, it may alreadybe seen from FIG. 6 that the actual membrane area 35 only makes up for arelatively small proportion of the total area of the pixel, and that inthis implementation, the fill factor is below 50%.

As may be seen in FIG. 6, FIG. 8 b or FIG. 10 a, the contact plug 26 bis connected to the membrane 10 via a thin arm 20, or 76 b. In additionto providing mechanical support and electrical supply, the arm 20, or 76b, also serves to thermally insulate the membrane 10 from the contactplug 26 b. Its long length and its small cross-sectional area ensure ahigh thermal resistance between the membrane 10 and the substrate.

As was already described, it is desirable to make the pixels as small aspossible. A direct comparison of FIGS. 10 a and 10 b shows that nosatisfactory solution may be found for this issue with pixels ofconventional technology. With the scaled pixel in FIG. 10 b, the contactplugs 26 a,b take up a disproportionately large share in the total pixelarea. This is due to the fact that the metal of the plug projects beyondits opening through the membrane 10 by x, additionally, the membrane 10is typically larger than the overlap x by a factor of y. With apredefined total area, the proportion of an active area on the membrane10 becomes smaller, the fill factor decreases, and a sensitivity of thepixels to the IR radiation also decreases as a consequence.

SUMMARY

According to an embodiment, a bolometer may have: a membrane including afirst ridge and a second ridge for thermal insulation; a first spacer; asecond spacer, the membrane including a resistive layer and a contactlayer, the contact layer including, at a side facing a foundation, afirst contact region at which the first spacer electrically contacts thecontact layer, and a second contact region at which the second spacerelectrically contacts the contact layer, and the first and secondspacers keeping the membrane at a predetermined distance from thefoundation, and the first ridge being connected to the first spacer, andthe second ridge being connected to the second spacer, and the contactlayer being laterally interrupted by a gap, so that the contact layer issubdivided at least into two parts, the first part of which includes thefirst contact region, and the second part of which includes the secondcontact region, and no direct connection existing within the contactlayer from the first contact region to the second contact region, andthe resistive layer being in contact with the first part of the contactlayer and to the second part of the contact layer.

According to another embodiment, a method of producing a bolometer mayhave the steps of: a) providing a substrate; b) depositing a sacrificiallayer onto the substrate; c) forming a first through opening and asecond through opening; d) forming first and second spacers in the firstand second through the openings; e) applying a contact layer such thatthe contact layer includes, at a side facing the substrate, a firstcontact region at which same is contacted by the first spacer, and asecond contact region at which same is contacted by the second spacer;f) patterning the contact layer so as to form a gap within same, so thatthe contact layer is subdivided into two parts, the first part of whichincludes the first contact region, and the second part of which includesthe second contact region, and no direct connection existing within thecontact layer from the first contact region to the second contactregion; g) applying a resistive layer such that the resistive layer isin contact with the first part of the contact layer and with the secondpart of the contact layer, the resistive layer and the contact layerforming a membrane of the bolometer; h) patterning an outline of themembrane; and i) patterning the membrane in order to form within same afirst ridge and a second ridge for thermal insulation, the first ridgebeing in contact with the first spacer, and the second ridge being incontact with the second spacer; j) removing the sacrificial layer.

According to another embodiment, a method of producing a bolometer mayhave the steps of: a) providing a substrate; b) depositing a sacrificiallayer onto the substrate; c) forming a first through opening and asecond through opening; d) forming a first spacer within the firstthrough opening and a second spacer within the second through opening;e) laterally applying a resistive layer such that the resistive layer isnot in contact with the conductive material within the first and secondthrough the openings; f) applying an insulating layer on a side of theresistive layer which faces away from the substrate, so that theinsulating layer leaves the resistive layer open at a first contactpoint and at a second contact point; g) applying a contact layer suchthat the contact layer includes, at a side facing the substrate, a firstcontact region at which same is contacted by the first spacer, and asecond contact region at which same is contacted by the second spacer,and such that the contact layer is in contact with the first contactpoint and with the second contact point of the resistive layer; h)patterning an outline of the membrane; i) patterning the membrane inorder to form within same a first ridge and a second ridge for thermalinsulation, the first ridge being in contact with the first spacer, andthe second ridge being in contact with the second spacer; j) patterningthe contact layer in order to form at least one gap within same, so thatthe contact layer is subdivided into at least two parts, the first partof which includes the first contact region and the first contact pointof the resistive layer, and the second part of which includes the secondcontact region and the second contact point of the resistive layer, andno direct connection existing within the contact layer from the firstcontact region to the second contact region; k) removing the sacrificiallayer.

The present invention is based on the finding that while using processsteps which are customary, for example, in CMOS technology, a pixelstructure may be produced which enables noticeable scaling.

Fundamental characteristics of an approach may be summarized, by way ofexample, as follows.

For example a CMOS wafer, which in the region of membrane 10 of thebolometer comprises a reflector, e.g. in the form of an Al layer, mayserve as a starting substrate. In the region of the contact plugs orspacers, one terminal pad (made of Al, for example) is connected to onereadout circuit, respectively. This substrate has a sacrificial layerdeposited thereon, for example an amorphous silicon layer (a-Si layer)of a thickness of approx. 2.5 μm. This may be performed, for example, ina CVD process (CVD=chemical vapor deposition), possibly assisted byplasma.

Subsequently, a first protective layer is deposited (e.g. a thin layerof silicon oxide is deposited by a CVD process; approx. 50-200 nm), sothat a layer sequence of a first protective layer/sacrificial layerresults. Possibly, a stress-compensated layer of, e.g., oxide andnitride is deposited instead. The layer sequence is now opened in theregion of the spacers. This may be performed, for example, by an etchingprocess, which comprises exposing, by means of photo technique, a smallcontact opening (of e.g. approx. 0.5×0.5 μm² to 1.5×1.5 μm²) in a resistmask. Thereafter, the layer sequence with the resist mask is etchedanisotropically, i.e. perpendicularly, so that a hole extends as fardown as the terminal pad (metal terminal of the readout circuit).Possibly the sacrificial layer underneath the first protective layer maybe slightly undercut, so that the first protective layer overhangsslightly. A thin intermediate layer, for example of Ti/TiN (e.g. 20nm/80 nm), is sputtered, so that a bottom and a wall of holes are atleast partially covered. A conductive material is deposited thereon (forexample tungsten by a CVD process) until the hole is completely filledup to a surface. For example by a CMP method (CMP=chemical mechanicalpolishing), the conductive material is polished off the surface(including the intermediate layer). The hole remains filled up with theconductive material in the process. The first protective layer is onlyslightly polished, but not fully removed.

The result is a fundamental structure on the basis of which twodifferent ways of continuing the process are possible.

Process Sequence A

A contact layer, e.g. a thin Ti/TiN layer, is deposited onto thefundamental structure and is patterned. A temperature-sensitiveresistive layer (consisting of a-Si, possibly of vanadium oxide (Vo_(x))or an organic semiconductor) is deposited thereon. The actual measuringresistor of the bolometer is formed by the resistive layer above a smallinterstice (gap) in the contact layer. To obtain as good a thermalinsulation as possible of the measuring resistor from the spacers and,therefore, from the foundation, in this kind of processing, the gap isadvantageously arranged as centrally between the spacers as possible.

By implementing the contact layer accordingly, for example by suitablyselecting the layer thickness and/or the layer material, the membranecomprises a layer resistance of 377Ω/□ and is therefore suitable as aλ/4 absorber, independently of the actually higher resistance of theresistive layer.

The resistive layer is now also patterned (for example using lithographyand an etching step). Next, a second protective layer (covering layer,for example consisting of oxide, possibly of an organic material) isdeposited and patterned, so that all of the layers above the sacrificiallayer are removed between the membranes, for example in a bolometerarray, and between the support arms and the associated membrane. Theresistive layer remains protected all around by the second protectivelayer and/or an organic covering layer.

At this point, the sacrificial layer is completely removed through theresulting openings. An etching process, for example using XeF₂, which isdescribed in Chu, P. B.; J. T. Chen; R. Yeh; G. Lin; J. C. P. Huang; B.A. Warneke; K. S. J. Pister “Controlled PulseEtching with XenonDifluoride”; 1997 International Conference on Solid State Sensors andActuators-TRANSDUCERS '97, Chicago, USA, June 16-19, p. 665-668, andwhich removes only the sacrificial layer at a high rate in an isotropic,i.e. non-directional manner, but with a high level of selectivity withregard to, e.g., oxide and organic materials, is particularly suitablefor this purpose. This is effective, in particular, when the sacrificiallayer comprises amorphous silicon. Consequently, the membrane is bared,and is supported and contacted only by the spacers. The resistive layer,which is protected on all sides, is not etched in this exemplaryprocess. The membrane is supported on the spacers. The material of thespacers does not project beyond the resistive layer.

This approach uses only a small number of process steps for realizing abolometer structure. In the following, alternative processing will bedescribed which exhibits the additional advantage of as large a surfacearea of the active resistive layer as possible.

Process Sequence B

Starting from the same fundamental structure as prior to the processsequence A, a thin resistive layer (e.g. of amorphous silicon, VO_(x),organic semiconductor) and an insulating layer (for example of oxide)are deposited. Subsequently, these two layers are patterned, so that thespacers which consisted of tungsten, for example, are bared. In order toadapt the layer resistance of the membrane, a contact layer (for examplea thin layer of TiN, 3-15 nm) is applied, possibly followed by a secondprotective layer, which may comprise an oxide, for example. Forthermally insulating the membrane, connections to the spacers are nowreduced to two narrow ridges. This may be performed, for example, by asequence of etching steps. When implementing the ridges, care has to betaken to ensure, on the one hand, that said implementation enables ahigh fill factor, and on the other hand, that the membrane is supportedin a mechanically stable manner.

At this point in time, the contact layer contacts both spacers with alow resistance in parallel with the actual resistive layer. The contactlayer is therefore interrupted, in two small regions (ridges), such thatparallel current conduction through the contact layer is prevented. Thismay be performed, for example, in a further etching step.

The entire structure is then passivated by a thin protective layer (forexample by an oxide layer) so as to protect the resistive layer.Finally, the sacrificial layer is removed, and thus, the membrane isbared. In this process sequence, too, an isotropic etching process usingXeF₂ may be used, for example.

Alternatively, the sacrificial layer may be removed already prior todefining the ridges and to insulating the contact layer. In this case,the resistive layer is protected on all sides, even without anyadditional passivation, from an attack of the etching process comprisingXeF₂ which is used by way of example.

Essential advantages of an inventive processing therefore include thefacts that the spacers may be scaled to have clearly smaller dimensionsand still exhibit sufficient adhesion to the membrane 10. Therefore, noopenings in the membrane 10 and overlaps x and y are necessary as wasthe case with plugs 26 a,b; see FIG. 9.

In other words, the spacers adjoin, or end at, the bottom of the contactlayer without pushing through the contact layer.

In addition, the inventive processing enables production of bolometersor bolometer arrays with clearly smaller pixel sizes at lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be detailed subsequentlyreferring to the appended drawings, in which:

FIGS. 1 a-i show steps of producing a bolometer in accordance withprocess sequence A of the present invention, and top views of thebolometer;

FIGS. 2 a-j show steps of producing a bolometer in accordance withprocess sequence B of the present invention, and top views of thebolometer;

FIGS. 3 a-g show steps of producing a bolometer using a changed processorder;

FIG. 4 a shows a top view of a membrane comprising contact regionswithout any overlap;

FIG. 4 b shows a top view of a scaled membrane having contact regionswithout any overlap;

FIG. 4 c shows a cross-sectional view of part of a membrane and aspacer;

FIGS. 5 a-b show cross-sectional views of conventional microbolometerstructures;

FIG. 6 shows a perspective view of a conventional structure comprising amembrane;

FIG. 7 shows a perspective view of a conventional structure comprising amembrane on two contact plugs with a metal overlap;

FIG. 8 a shows a cross-sectional view of a conventional structure havinga contact plug and a part of a membrane as well as remaining sacrificiallayer;

FIG. 8 b shows a top view of the conventional structure of FIG. 8 a;

FIG. 9 shows a cross-sectional view of a contact plug and a part of amembrane and marked overlaps;

FIG. 10 a shows a top view of a membrane comprising conventionalcontacting with contact plugs; and

FIG. 10 b shows a top view of a scaled membrane comprising conventionalcontacting with contact plugs.

DETAILED DESCRIPTION OF THE INVENTION

Before the present invention will be explained below in more detail withreference to the drawings, it shall be noted that identical elements inthe figures are given identical or similar reference numerals, and thatrepeated descriptions of these elements shall be omitted.

FIGS. 1 a-h show cross-sectional views of a sequence of steps for afirst embodiment of the present invention, and FIG. 1 i shows acorresponding top view with a marked sectional plane 199 of thecross-sectional views.

FIG. 1 a shows a cross section of a substrate 100 (e.g. CMOS wafer)which has a terminal pad 110 a and a terminal pad 110 b depositedthereon, and, additionally, a reflector 120 applied to it. A connectionof the terminal pad 110 a and of the terminal pad 110 b to an underlyingCMOS circuit is not shown. Both terminal pads 110 a, 110 b serve thepurpose of subsequent contacting of the bolometer.

In a subsequent step, a sacrificial layer 130 and a first protectivelayer 140, as shown in FIG. 1 b, are deposited onto the structure shownin FIG. 1 a. The sacrificial layer 130 is removed again in a later step,and it comprises a layer thickness, so that the bolometer represents aλ/4 absorber. In an advantageous embodiment, the sacrificial layer 130comprises amorphous silicon, and the first protective layer 140comprises an oxide.

As is shown in FIG. 1 c, through openings 150 a′ and 150 b′ through theprotective layer 140 and through the sacrificial layer 130 are producedin a next step. The through opening 150 a′ is positioned such that itends on the terminal pad 110 a, and the through opening 150 b′ ispositioned, by analogy therewith, such that it ends on the terminal pad110 b. In a next step, the through opening 150 a′ and the throughopening 150 b′ are filled up with a conductive material, and anymaterial which juts out is removed, so that a planar surface 142results.

As is shown in FIG. 1 d, a contact layer 160 is deposited onto thesurface 142 in a subsequent step. In a next step, which is shown in FIG.1 e, the contact layer 160 is patterned, and a resistive layer 170 isdeposited. As a result, the patterned contact layer 160 comprises a gap162 which separates a first part 160 a from a second part 160 b of thecontact layer 160. To achieve as good a thermal insulation of the gap162 from the spacers 150 a and 150 b as possible, the minimum distancefrom the first spacer 150 a to the gap 162 should be identical, as faras possible, to a minimum distance from the second spacer 150 b to thegap 162.

Advantageously, the gap 162 has such a width that the measuring resistorof the bolometer ranges from, e.g., 0.1 kΩ to 1 GΩ, and advantageouslyfrom 1 kΩ to 100 MΩ.

The resistive layer 170 is subsequently patterned, and a secondprotective layer 180 is applied. This is shown in FIG. 1 f. As is shownin FIG. 1 g, the surface of the bolometer is patterned in a subsequentstep, so that the second protective layer 180 and the contact layer 160end essentially flush with the spacers 150 a and 150 b. This patternedresistive layer 170 extends to an inner region of a membrane surface 192which will form later on, so that the patterned resistive layer 170 hasno contact to edge regions 190 a and 190 b. In this step, the firstprotective layer 140 is also patterned, so that the first protectivelayer 140 is located between the contact layer 160 and the sacrificiallayer 130.

In a last step, which is shown in FIG. 1 h, the sacrificial layer 130 isremoved. The resulting bolometer comprises a membrane 10 which has alayer sequence comprising the first protective layer 140, the contactlayer 160 with the first part 160 a and the second part 160 b, theresistive layer 170, and the second protective layer 180. The bolometercomprises a surface 192 which ends essentially flush with the spacers150 a and 150 b. The spacers 150 a and 150 b have a height 198 selectedsuch that the membrane 10 is kept at a distance 198, and that thedistance 198 ideally corresponds to a quarter of the wavelength to bedetected.

FIG. 1 i shows a top view of the surface 192 of the bolometer withcontact areas at which the spacers 150 a and 150 b contact the membrane10. A dashed line 199 marks the cross-sectional plane, which passes thegap 162 and is depicted in a viewing direction 81 in FIGS. 1 a to 1 h.

FIGS. 2 a to 2 g show a second embodiment of the present invention.FIGS. 2 a to 2 f show cross-sectional views with regard to a sequence ofsteps of producing a bolometer, and FIG. 2 g shows a corresponding topview with a marked sectional plane 230 of the cross-sectional views. Thefirst steps of the second embodiment correspond to a sequence of stepsdescribed in FIGS. 1 a to 1 c. Therefore, explanations on the individualsteps will be omitted at this point.

The structure shown in FIG. 1 c initially has a resistive layer 170 andan insulating layer 210 applied thereon, so that the structure shown inFIG. 2 a is obtained. FIG. 2 a further shows the substrate 100, thefirst terminal pad 110 a with the first spacer 150 a, the secondterminal pad 110 b with the second spacer 150 b, the reflector 120, thesacrificial layer 130, and the first protective layer 140.

Subsequently, the resistive layer 170 and the insulating layer 210 arepatterned, and the result is shown in FIG. 2 b. The patterning isperformed such that the resistive layer 170 has no contact to thespacers 150 a and 150 b, and that additionally, the insulating layer 210does not fully cover the resistive layer 170, so that a first contactpoint 175 a and a second contact point 175 b remain open.

As FIG. 2 c shows, a contact layer 160 is applied thereon whichestablishes a contact between the resistive layer 170 and the spacers150 a and 150 b.

Subsequently (as is shown in FIG. 2 d), the contact layer 160 isinitially patterned, which comprises, in particular, cutting through thecontact layer 160 twice by columns 250 a and 250 b. As a result, thecontact layer 160 is divided up into a layer 160 a, which is in contactwith the spacer 150 a and with the resistive layer 170, a layer 160 b,which is in contact with the spacer 150 b and with the resistive layer170, and a layer 160 c, which is separate from the layer 160 a and thelayer 160 b. Consequently, the layers 160 a and 160 b are separate, sothat an electric current from the first spacer 150 a to the secondspacer 150 b passes the resistive layer 170. In addition, the layer 160c is not in contact with the resistive layer 170 and has the task ofadjusting a layer resistance of the membrane 10 in accordance with thecharacteristic impedance of an electromagnetic wave in air.

Subsequently, a second protective layer 180 is applied to the contactlayer 160. The result is shown in FIG. 2 e. Further patterning of theprotective layer 180 defines a surface 192 of the membrane 10 of thebolometer.

In a next step, the columns 220 a and 220 b shown in FIG. 2 g arecreated. The columns 220 a and 220 b cut through the membrane 10comprising the first protective layer 140, the resistive layer 170, theinsulating layer 210, the contact layer 160, and the second protectivelayer 180. Since a sectional plane belonging to the cross-sectionalviews 2 a to 2 f does not cross the columns 220 a and 220 b, the columns220 a and 220 b are not shown in the cross-sectional views of FIGS. 2 ato 2 f. In the top view of FIG. 2 g, the sectional plane is marked bythe dashed line 230. The arrows 240 show the viewing direction of thesectional plane.

In a last step, shown in FIG. 2 f, the first and second protectivelayers (140, 180) are patterned such that the surface 192 of themembrane 10 ends essentially flush with the spacers 150 a and 150 b, andeventually, the sacrificial layer 130 is removed.

In a further embodiment, patterning of the contact layer 160 isperformed asymmetrically, i.e. the contact layer is separated only by agap. In this embodiment, the steps leading up to the structure shown inFIG. 2 c are identical to the previously described embodiment, andrepetition of the description will be dispensed with at this point.

In this embodiment, the structure shown in FIG. 2 c is patterned asshown in FIG. 2 h, i.e., in particular, only a gap 250 is created whichcuts through the contact layer 160. This results in a layer 160 a whichis in contact with the spacer 150 a and to the resistive layer 170, alayer 160 b which is in contact with the spacer 150 b and with theresistive layer 170. Consequently, the layers 160 a and 160 b areseparated in this case, too, so that an electric current from the firstspacer 150 a to the second spacer 150 b passes the resistive layer 170.In this embodiment, the layer resistance of the membrane 10 may occur,in accordance with the characteristic impedance of an electromagneticwave in air, by adapting, e.g., the layer 160 b or the layer 160 a.

The steps (depositing the second protective layer 180, and patterning)shown in FIG. 2 i again correspond to the steps described in FIG. 2 e.The same applies to the other steps (creating the columns 220 a and 220b, further patterning and removing the sacrificial layer 130), whichwere already described in the context of FIG. 2 f. Therefore, renewedrepetition will be dispensed with at this point. Finally, FIG. 2 j showsthe resulting bolometer comprising the membrane 10 and the asymmetricgap 250.

The indicated order of the steps is only an example and may be varied infurther embodiments. For example, creating the columns 220 a and 220 band/or forming the ridges 76 a and 76 b may also take place at the end.The columns 220 a,b are implemented such that as large a region aspossible of the resistive layer 170 is thermally insulated from thespacers 150 a,b, and that, the fill factor thus is as large as possible.At the same time, however, they are to provide sufficient support forthe membrane 10.

In addition to the process order discussed so far, a reversal is alsofeasible wherein the contact layer 160 is deposited prior to theresistive layer 170. This is shown in FIGS. 3 a to 3 g. Cross-sectionalviews are shown, again, wherein the first steps again correspond to asequence of steps as was described in FIGS. 1 a to 1 c. A repetition ofthe explanations on the individual steps shall be omitted again at thispoint.

The structure shown in FIG. 3 a corresponds to the structure shown inFIG. 1 c, and comprises the first protective layer 140 as the top layer.In this embodiment, the contact layer 160 is deposited and patterned asthe first further layer. The result is shown in FIG. 3 b. The patterningis performed such that on the one hand, the contact layer 160 endsessentially flush with the spacers 150 a and 150 b, and on the otherhand, it comprises a gap 250 which divides the contact layer 160 intothe layer 160 a and the layer 160 b. The layer 160 a is in contact withthe spacer 150 a, and the layer 160 b is in contact with the spacer 150b.

As is shown in FIG. 3 c, the insulating layer 210 is deposited thereonand patterned, so that the insulating layer essentially fills up the gap250 and, in addition, leaves open the first contact point 175 a at thelayer 160 a and the second contact point 175 b at the layer 160 b.

As is shown in FIG. 3 d, the resistive layer 170 is deposited thereonand patterned, so that the resistive layer 170 ends essentially flushwith the spacers 150 a and 150 b.

As is shown in FIG. 3 e, the second protective layer 180 is againdeposited thereon and patterned, so that the membrane 10 with thesurface 192 is defined. The result is shown in FIG. 3 f. As a last step,the sacrificial layer 130 is again removed, so that the structure ofFIG. 3 g results.

FIG. 4 a shows a top view of the membrane 10 comprising contact areas,where the spacers 150 a and 150 b contact the membrane 10.

FIG. 4 b shows the scaled membrane 10, i.e. a membrane 10 which isreduced in size accordingly. In this context, unlike the prior art , thecontact areas 150 a and 150 b also scale in accordance with a size ofthe membrane 10. In both cases, the membrane 10 exhibits no overlap overcontact areas at which the spacers 150 a and 150 b come into contactwith the membrane 10.

FIG. 4 c shows a scaled contact between the membrane 10 and the spacer150 b. The membrane 10 is positioned on the spacer 150 b without anyoverlap.

As compared to the prior art , an inventive method is advantageous inseveral respects. For example, inventive processing using the spacers150 a and 150 b, which advantageously comprise tungsten, and using thesacrificial layer 130, which advantageously comprises amorphous silicon(a-Si), enables reduction of the size of the IR-sensitive pixel. Aconventional process using photosensitive polyimide has a minimum holesize which must be larger than approx. 3 μm. Even if smaller holes inthe polyimide were possible (e.g. by means of a multilayer mask ofphotoresist and oxide on the polyimide, which may then be opened usingan anisotropic etching process comprising oxygen plasma), said holescannot be filled up, or may only be insufficiently filled up, withtungsten, for example. The tungsten deposition using the CVD methodtypically requires temperatures of more than 450° C., at which thepolyimide is no longer stable.

On the other hand, utilization of a-Si as the sacrificial layer 130 isheat-resistant and enables depositing spacers 150 a and 150 b consistingof, e.g., tungsten, of a good quality, as are customary in CMOStechnology for multi-layer metallization. For example, holes having verysmall diameters and high aspect ratios (depth/diameter) may be etchedinto the a-Si layer, as is known from the production of trenches inDRAMs. The a-Si layer is stable, so that a relatively intense etch-backprocess, e.g. using Ar ions, is possible prior to depositing the contactlayer 160 (for example by sputtering Ti/TiN). This reduces a contactresistance between the spacers 150 a,b and the contact layer 160, andimproves the adhesion of the contact layer 160 to the spacers 150 a,b.

The resulting structure having the membrane 10 resting on the spacers150 a,b may be scaled to have small dimensions, since the process stepsmentioned (except for depositing and isotropically removing theexemplary a-Si sacrificial layer 130) may be gathered from any modernCMOS process. For example, a 0.25 μm process enables a diameter smallerthan 0.5 μm for the spacers 150 a,b, the support arms may be as wide asa diameter of the spacers 150 a,b, and they may have a distance of 0.25μm to the membrane 10.

Therefore, essential advantages of inventive processing are that thespacers 150 a,b may be scaled to have clearly smaller dimensions whilestill exhibiting sufficient adhesion to the membrane 10. Consequently,moving the spacers 150 a,b through the membrane 10, and an overlap bythe values of x and y are not necessary as was the case with plugs 26a,b. In an embodiment of the present invention, formation of ridges 76a,b may further be dispensed with, which results in a further increasein the fill factor and in improved mechanical stability.

In addition, inventive processing enables the production of bolometersor bolometer arrays with clearly smaller pixel sizes at lower cost.

Thus, pixels of 20×20 μm² or 15×15 μm² with a constantly high fillfactor are possible. The distance between the membranes 10 within abolometer array may be 0.5 μm, for example, so that a pixel pitch(distance from the center of a pixel to the center of another pixel) mayalso be 15-20 μm.

As was set forth above, two embodiments of the present invention arebased on two process flows. Both process flows may be summarized asfollows while indicating advantageous materials, layer thicknesses,methods used, etc.

Process Flow A

-   -   providing a CMOS disk with a passivated surface    -   depositing a metallic reflector 120 and two terminal pads 110 a,        110 b for a connection CMOS membrane, e.g. made of thin Al (e.g.        100-200 nm, therefore only small stage)    -   depositing a-Si approx. 2.5 μm (as a sacrificial layer 130)    -   possibly smoothing the surface by a CMP process    -   oxide deposition of a first protective layer 140 (approx. 200        nm)    -   defining through openings 150 a′ and 150 b′ by means of photo        technique (diameter approx. 0.5-1 μm)    -   oxide-etching, silicon-etching anisotropically, stop on pad        metal of terminal pads 110 a and 110 b    -   Ti/TiN barrier sputtering in the through openings 150 a′ and 150        b′    -   tungsten CVD process for filling up the through openings 150 a′        and 150 b′    -   CMP method for removing the tungsten and Ti/TiN from the surface    -   backsputtering    -   sputtering the contact layer 160; TiN thin (for layer resistance        of 377Ω/□)    -   etching the contact layer 160 using photo technique (removing        TiN underneath the actual resistor), forming a gap 162    -   depositing a-Si, doped for bolometer resistor 170    -   photo technique, etching a-Si, patterning the resistive layer        170    -   depositing oxide using a CVD process in order to form the second        protective layer 180 (approx. 30 nm)    -   photo technique for defining the membrane area, and baring the        terminal arms    -   etching the layers as far as into the a-Si sacrificial layer    -   removing the a-Si sacrificial layer 130, for example using        highly selective oxide (is hardly attacked), isotropic etching        in gaseous XeF₂.        Process Flow B    -   providing a CMOS disk with a passivated surface    -   depositing a metallic reflector 120 and two terminal pads 110 a        and 110 b for a connection CMOS membrane, e.g. made of thin Al        (e.g. 100-200 nm, therefore only small stage)    -   depositing a-Si approx. 2.5 μm (as a sacrificial layer 130)    -   possibly smoothing the surface by a CMP process    -   oxide deposition of a first protective layer 140 (approx. 200        nm)    -   defining through openings 150 a′ and 150 b′ by means of photo        technique (diameter approx. 0.5-1 μm)    -   oxide-etching, silicon-etching anisotropically, stop on pad        metal of terminal pads 110 a and 110 b    -   Ti/TiN barrier sputtering in the through openings 150 a′ and 150        b′    -   tungsten CVD process for filling up the through openings 150 a′        and 150 b′    -   CMP for removing the tungsten and Ti/TiN from the surface    -   backsputtering    -   depositing a-Si, doped for bolometer resistance 170    -   depositing oxide using a CVD process in order to form the        insulating layer 210 (approx. 30 nm)    -   photo technique for patterning the oxide of the insulating layer        210    -   photo technique for patterning the bolometer resistance 170    -   sputtering the contact layer 160; TiN thin (for layer resistance        of 377Ω/□)    -   depositing oxide using a CVD process as the second protective        layer 180 (approx. 30 nm)    -   photo technique for defining the narrow ridge regions 76 a and        76 b, etching oxide (second protective layer 180), TiN (contact        layer 160), a-Si (resistive layer 170), and again oxide (first        protective layer 140).    -   photo technique for insulating the TiN layer 160 of the membrane        10    -   etching oxide of the second protective layer 180 and TiN of the        contact layer 160, and creating the columns 250 a and 250 b    -   depositing oxide using a CVD process for protecting the contact        layer 160 (approx. 30 nm)    -   removing the a-Si sacrificial layer 130, for example using        highly selective oxide (is hardly attacked), isotropic etching        in gaseous XeF₂.

The materials indicated above are only examples which allow very goodprocessing. Some alternatives include the following replacements, forexample.

The sacrificial layer 130 of a-Si may alternatively be etched using ClF₃(chlorofluoride) or using an isotropic SF₆ plasma (sulfuric fluorideplasma). The sacrificial layer 130 may also comprise a heat-resistantpolymer (e.g. polyimide). The through openings 150 a′ and 150 b′ for thespacers 150 a and 150 b may then be etched with anisotropic O₂ plasma,the sacrificial layer 130 may also be removed using an O₂ plasma.

When the sacrificial layer 130 is removed in an etching step, it isimportant to protect the resistive layer 170 and/or the contact layer160 during the etching step. To this end, the presence of the protectivelayer 140 is advantageous. The material is advantageously selected suchthat it is not or hardly attacked in the step of removing thesacrificial layer 130. However, if there is a method available whichremoves the sacrificial layer 130 without attacking the resistive layer170 and/or the contact layer 160, the first protective layer 140 mayalso be dispensed with in a further embodiment.

The temperature-dependent resistive layer 170 may comprise, for example,a different semiconductor material (VO_(x), GaAs, organic semiconductor,or others). Instead of the silicon oxide layers, it is also possible touse layers of silicon nitride (or a combination of both).

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which fall withinthe scope of this invention. It should also be noted that there are manyalternative ways of implementing the methods and compositions of thepresent invention. It is therefore intended that the following appendedclaims be interpreted as including all such alterations, permutationsand equivalents as fall within the true spirit and scope of the presentinvention.

1. A bolometer comprising: a membrane; a first spacer; a second spacer, the membrane comprising a resistive layer, a first protective layer, a second protective layer, and a contact layer, the resistive layer and the contact layer extending between the first protective layer and the second protective layer with the first protective layer being located at a side of the membrane facing a foundation, the first protective layer including a first through hole and a second through hole, the contact layer comprising, at a side facing the foundation, a first contact region at which the first spacer extends through the first through hole in the first protective layer and electrically contacts the contact layer, and a second contact region at which the second spacer extends through the second through hole in the first protective layer and electrically contacts the contact layer, and the first and second spacers keeping the membrane at a predetermined distance from the foundation, the contact layer being laterally interrupted by a gap, so that the contact layer is subdivided at least into two parts, the first part of which comprises the first contact region, and the second part of which comprises the second contact region, and no direct connection existing within the contact layer from the first contact region to the second contact region, and the resistive layer being in contact with the first part of the contact layer and with the second part of the contact layer, wherein the membrane is patterned so that a first ridge and a second ridge for thermal insulation are provided in the membrane, the first ridge includes the first contact region in contact with the first spacer, and the second ridge includes the second contact region in contact with the second spacer.
 2. The bolometer as claimed in claim 1, wherein lateral ends of the membrane are substantially flush with the first spacer and the second spacer.
 3. The bolometer as claimed in claim 1, wherein the predetermined distance equals a quarter of an infrared wavelength.
 4. The bolometer as claimed in claim 1, wherein the contact layer comprises a layer thickness so that a layer resistance of the membrane corresponds to a characteristic impedance of electromagnetic waves in air.
 5. The bolometer as claimed in claim 1, wherein the foundation comprises a reflector.
 6. The bolometer as claimed in claim 1, wherein the membrane comprises, in a top view of a side facing away from the foundation, a substantially square shape, and wherein the first spacer and the second spacer are located at opposing corner points of the membrane.
 7. The bolometer as claimed in claim 1, wherein the gap comprises a width such that a resistance contribution to a measuring resistor of the bolometer, which is due to a current flowing between the first contact region and the second contact region, ranges approximately between 1 kΩ and 100 MΩ.
 8. The bolometer as claimed in claim 1, wherein a position of the gap is selected such that an electric current from the first spacer to the second spacer reaches the gap after having covered a certain distance, and wherein the distance covered is equal to a distance, as far as possible, covered by the electric current on its way from the gap to the second spacer.
 9. The bolometer as claimed in claim 1, wherein the membrane further comprises an insulating layer arranged between the resistive layer and the contact layer, and wherein the resistive layer is located on the side of the membrane which faces the foundation.
 10. The bolometer as claimed in claim 1, wherein the membrane further comprises an insulating layer arranged between the contact layer and the resistive layer, and wherein the contact layer is located on the side of the membrane which faces the foundation.
 11. The bolometer as claimed in claim 1, wherein the resistive layer comprises amorphous silicon or vanadium oxide.
 12. The bolometer as claimed in claim 1, wherein the contact layer comprises titanium nitride.
 13. The bolometer as claimed in claim 1, wherein the first spacer and/or the second spacer comprise tungsten or copper.
 14. The bolometer as claimed in claim 1, wherein the foundation further comprises a first terminal pad and a second terminal pad arranged to contact the first spacer and the second spacer, respectively.
 15. A method of producing a bolometer, comprising the steps of: a) providing a substrate; b) depositing a sacrificial layer onto the substrate; c) depositing a first protective layer on the sacrificial layer; d) forming a first through opening and a second through opening through the sacrificial layer and the first protective layer so as to extend to the substrate; e) forming first and second spacers in the first and second through openings; f) applying a contact layer such that the contact layer comprises, at a side facing the substrate, a first contact region at which same is contacted by the first spacer, and a second contact region at which same is contacted by the second spacer; g) patterning the contact layer so as to form a gap within same, so that the contact layer is subdivided into two parts, the first part of which comprises the first contact region, and the second part of which comprises the second contact region, and no direct connection existing within the contact layer from the first contact region to the second contact region; h) applying a resistive layer such that the resistive layer is in contact with the first part of the contact layer and with the second part of the contact layer, the resistive layer and the contact layer forming a membrane of the bolometer; i) depositing a second protective layer; j) patterning an outline of the membrane; and k) patterning the membrane in order to form within same a first ridge and a second ridge for thermal insulation, the first ridge being in contact with the first spacer, and the second ridge being in contact with the second spacer; l) removing the sacrificial layer.
 16. The method as claimed in claim 15, wherein a sequence of the steps is defined by the steps of depositing the sacrificial layer onto the substrate, applying the contact layer, patterning the contact layer, applying the resistive layer, and patterning the outline of the membrane.
 17. The method as claimed in claim 15, further comprising a step of depositing a reflector between the steps of providing the substrate and depositing the sacrificial layer.
 18. The method as claimed in claim 15, further comprising, between the steps of patterning the contact layer and applying the resistive layer, a step of applying an insulating layer such that the insulating layer leaves open the first part at a first contact point and the second part at a second contact point.
 19. The method as claimed in claim 15, wherein the step of applying the sacrificial layer is performed such that the sacrificial layer comprises a layer thickness which corresponds to a quarter of an infrared wavelength.
 20. The method as claimed in claim 15, wherein the step of applying the contact layer is performed such that the contact layer comprises a layer thickness such that the sheet resistance of the membrane corresponds to a characteristic impedance of an electromagnetic wave in air.
 21. The method as claimed in claim 15, wherein the step of providing the substrate comprises the steps of: a1) providing the substrate; and a2) forming a first terminal pad and a second terminal pad on the substrate, the first terminal pad contacting the first spacer, and the second terminal pad contacting the second spacer.
 22. The method as claimed in claim 15, wherein the step of applying the resistive layer comprises using amorphous silicon oxide or vanadium oxide.
 23. The method as claimed in claim 15, wherein the step of applying the contact layer comprises using titanium nitride, and the step of forming the first and second spacers comprises using tungsten or copper.
 24. The method as claimed in claim 15, wherein the step of depositing the sacrificial layer comprises chemical vapor deposition.
 25. The method as claimed in claim 15, wherein the step of depositing the first protective layer and the step of depositing the second protective layer are performed such that the first and second protective layers comprise oxide, the step of applying the sacrificial layer is performed such that the sacrificial layer comprises amorph silicon, and the step of removing the sacrificial layer comprises selective isotropic etching the sacrificial layer.
 26. A method of producing a bolometer, comprising the steps of: a) providing a substrate; b) depositing a sacrificial layer onto the substrate; c) depositing a first protective layer on the sacrificial layer; d) forming a first through opening and a second through opening through the sacrificial layer and the first protective layer so as to extend to the substrate; e) forming a first spacer within the first through opening and a second spacer within the second through opening; f) laterally applying a resistive layer such that the resistive layer is not in contact with conductive material within the first and second through openings; g) applying an insulating layer on a side of the resistive layer which faces away from the substrate, so that the insulating layer leaves the resistive layer open at a first contact point and at a second contact point; h) applying a contact layer such that the contact layer comprises, at a side facing the substrate, a first contact region at which same is contacted by the first spacer, and a second contact region at which same is contacted by the second spacer, and such that the contact layer is in contact with the first contact point and with the second contact point of the resistive layer; i) patterning an outline of the membrane; j) patterning the membrane in order to form within same a first ridge and a second ridge for thermal insulation, the first ridge being in contact with the first spacer, and the second ridge being in contact with the second spacer; k) patterning the contact layer in order to form at least one gap within same, so that the contact layer is subdivided into at least two parts, the first part of which comprises the first contact region and the first contact point of the resistive layer, and the second part of which comprises the second contact region and the second contact point of the resistive layer, and no direct connection existing within the contact layer from the first contact region to the second contact region; l) depositing a second protective layer; and m) removing the sacrificial layer.
 27. The method as claimed in claim 26, wherein a sequence of steps is defined by the steps of forming the first spacer, laterally applying the resistive layer, applying the insulating layer, applying the contact layer, patterning the outline of the membrane, and patterning the membrane.
 28. The method as claimed in claim 26, further comprising, between the steps of providing the substrate and depositing the sacrificial layer: depositing a reflector; forming a first terminal pad and a second terminal pad on the substrate; and the first terminal pad contacting the first spacer, and the second terminal pad contacting the second spacer.
 29. The method as claimed in claim 26, wherein the step of depositing the sacrificial layer is performed such that the sacrificial layer comprises a layer thickness which corresponds to a quarter of an infrared wavelength.
 30. The method as claimed in claim 26, wherein the step of depositing the first protective layer being performed between the steps of depositing the sacrificial layer and forming the first through opening and a second through opening, and the step of depositing the second protective layer being performed between the steps of patterning the contact layer and removing the sacrificial layer.
 31. The method as claimed in claim 26, wherein the step of patterning the contact layer comprises the step of forming a second gap, so that the contact layer further comprises a third part, and wherein the step of applying the contact layer is performed such that the third part comprises a layer thickness such that a sheet resistance of the membrane corresponds to a characteristic impedance of an electromagnetic wave in air.
 32. The method as claimed in claim 26, wherein the step of depositing the first protective layer and the step of depositing the second protective layer are performed such that the first and second protective layers comprise oxide, the step of applying the sacrificial layer is performed such that the sacrificial layer comprises amorph silicon, and the step of removing the sacrificial layer comprises selective isotropic etching the sacrificial layer. 